gh-128421: Add locking to most frame object functions#131479

colesbury · 2025-03-19T20:32:54Z

This makes more operations on frame objects thread-safe in the free threaded build, which fixes some data races that occurred when passing exceptions between threads.

However, accessing local variables or the line number of a frame from another thread while its still executing is not thread-safe and may crash the interpreter.

Issue: data races in frame inspection and tracebacks #128421

This makes more operations on frame objects thread-safe in the free threaded build, which fixes some data races that occurred when passing exceptions between threads. However, accessing local variables from another thread while its running is still not thread-safe and may crash the interpreter.

Objects/frameobject.c

colesbury · 2025-03-21T14:26:03Z

I added the additional critical sections, although I'm pretty ambivalent about having them in the C APIs.

kumaraditya303

LGTM

The recent PR pythongh-131479 added locking to `take_ownership` in the free threading build. The cost is not really the locking -- that path isn't taken frequently -- but the inlined code causes extra register spills and slows down RETURN_VALUE, even when it's not taken. Mark `take_ownership` as `Py_NO_INLINE` to avoid the regression.

The recent PR pythongh-131479 added locking to `take_ownership` in the free threading build. The cost is not really the locking -- that path isn't taken frequently -- but the inlined code causes extra register spills and slows down RETURN_VALUE, even when it's not taken. Mark `take_ownership` as `Py_NO_INLINE` to avoid the regression. Also limit locking in PyFrameObject to Python functions, not the C API.

The recent PR pythongh-131479 added locking to `take_ownership` in the free threading build. The cost is not really the locking -- that path isn't taken frequently -- but the inlined code causes extra register spills and slows down RETURN_VALUE, even when it's not taken. Mark `take_ownership` as `Py_NO_INLINE` to avoid the regression. Also limit locking in PyFrameObject to Python functions, not the C API. PyFrame_GetCode is called frequently by coverage and tracing tools.

bedevere-appbot mentioned this pull request Mar 19, 2025
data races in frame inspection and tracebacks #128421
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colesbury added skip news topic-free-threading labels Mar 19, 2025

colesbury force-pushed the gh-128421-frame branch from 44f8c85 to c6f3c86Compare March 19, 2025 20:41

colesbury marked this pull request as ready for review March 19, 2025 21:20

colesbury requested a review from markshannon as a code owner March 19, 2025 21:20

bedevere-appbot added the awaiting core review label Mar 19, 2025

colesbury requested a review from kumaraditya303 March 19, 2025 21:20

kumaraditya303 reviewed Mar 20, 2025
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kumaraditya303 reviewed Mar 20, 2025
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